1. Field of the Invention
This invention relates to an improved method of making N-{[(4-chlorophenyl) amino] carbonyl}-2,6-difluorobenzamide ("Dimilin").
Dimilin, a trademark of Thompson-Hayward Chemical Company, is an important insect growth regulator, particularly for gypsy moth control. The final synthetic steps used to prepare this compound comprises treating 2,6-difluorobenzonitrile with concentrated sulfuric acid to convert it to the benzamide, and subsequently condensing with p-chlorophenyl isocyanate to form the desired product.
Since these reactions are run in a solvent, it is desired to provide an improved process in which the same solvent may serve as the extraction solvent for the benzamide, as the in situ reaction solvent for the condensation reaction, and as the crystallization solvent for the product.
Such a selective solvent thus should be capable of extracting the relatively insoluble benzamide from the aqueous, acid solution. It should have a high boiling point so that the condensation reaction may be run at elevated temperatures. Finally, it should dissolve the product selectively to enable crystallization to take place easily. These and other attributes and features of a selective solvent in accordance with the invention will be made apparent from the following, more particular, description of the invention.